Membrane-bound Angiotensin-converting Enzyme from Rat Lung

Abstract

Abstract Angiotensin-converting enzyme was found in rat lung predominantly in association with membranous subcellular particles. The converting enzyme was solubilized from a particulate fraction of rat lung that sedimented between 775 and 54,000 x g with sodium deoxycholate and was subsequently purified with DEAE-cellulose and Sephadex G-200 chromatography. The fraction with converting enzyme activity obtained from Sephadex G-200 chromatography had an estimated molecular weight of 270,000 as observed by gel filtration. Analytical disc gel electrophoresis of this preparation showed a single band. The specific converting enzyme activity of the purified preparation was 17.6 µmoles per min per mg with hippurylhistidylleucine as substrate and 1.8 µmoles per min per mg with angiotensin 1 as substrate. This represented a greater than 100-fold purification of the activity of subcellular particles. Sodium chloride was required for activation of the enzyme, and it was inhibited by EDTA, bradykinin potentiating factor-nonapeptide, and angiotensin 2, but not by histidylleucine. The purified preparation was free of carboxypeptidase activity on angiotensin 1. The distribution of converting enzyme activity in subcellular particles from rat lung paralleled that of 5'-AMPase activity which has been associated with pinocytotic vesicles of endothelial membranes. Little or no converting enzyme activity was present in particles obtained from lung lavage.